Take me back to Constantinople
No, you can't go back to Constantinople
Now it's Istanbul, not Constantinople
Istanbul (Not Constantinople), first recorded by The Four Lads in 1953
On this day in 1453, the Ottomans, under the command of Sultan Mehmet II, took Constantinople, ending the more than 1100 year-old Byzantine Empire.
The name Constantinople ("City of Constantine") comes from the name of the Byzantine emperor Constantine, who around 330 A.D. rebuilt the earlier city of Byzantium.
This mosaic from Haghia Sophia, built around 532 A.D. by the emperor Justinian in Constantinople shows the emperors Justinian (left) and Constantine (right) presenting to the Virgin Mary what appear to be models of Haghia Sophia and the city, respectively. Almost immediately after the city fell, the Ottomans converted Haghia Sophia to a mosque, but rather than destroy its mosaics, they plastered over them. Haghia Sophia, with its mosaics restored, is now a museum. This picture is from a slide I took in 1987.
To its residents, Constantinople was the city without a need to further specify. Thus, the best explanation for the obscure origin of its present name Istanbul, which actually has no meaning in Turkish, is the Greek phrase Ης την Πόλη (Is tin Poli = "to the city"). It is believed that the Ottoman Turks, upon repeatedly hearing that phrase, started using it as a name.
This is supported by what appears to be a similar derivation: Istanköy, the Turkish name of the Greek island of Kos. (Köy means village, but istan is meaningless.)
However, Constantinople didn't become Istanbul right after its fall. It had many other names throughout the Ottoman centuries, including Dersaadet (used until the early 20th century), Islambol ("Plenty of Islam", obviously a derivation from the meaningless Istanbul) and Kostantiniye, "City of Kostantin" from Arabic.
Sultan Mehmet II, a.k.a. Mehmet the Conqueror, in a painting attributed to the Venetian painter Gentile Bellini (1429-1507). The original is in the National Gallery in London, England. For a discussion of this painting in a historical context, read this Guardian article.
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Many thanks to Yorgi Sangiouloglou for his help with Greek.